Method of anticipating failure in oil treating systems



0a. 16, 1934. 1.. DE FLOREZ 1,977,177

METHOD OF ANTICIPATING FAILURE IN OIL TREATING SYSTEMS Filed March 19. 1931 2 Sheets-Sheet l F ZF [Z I F 1 Luis d9 Her-e5 INVENTOR BY )(O-gmit M /m ATTORNEYS Oct. 16, 1934*. DE FLOREZ 1,977,177

METHOD OF ANTICIPATING FAILURE IN OIL TREATING SYSTEMS 2 Sheets-Sheet 2 hm ATTORNEYS Patented s. 16, 1934 1 UNITED sra'rss PATENT orrics 1.911.111 amnion or sn'rrcreamo rarnuas' n: on. mama SYSTEMS.

Luis dc Flores, Pomfret, Conn. Application March s, 1m. Serial No. szsszs scum. (oi. m-m

This invention relates to thesafeguarding of pressure vessels and conduits against breakdown due to impairment of the walls thereof by corrosion and/or erosion. In its broader and more 8 general aspects the invention is concerned with a method of treating the walls of such receptacles whereby a diminution of the thickness thereof due. to corrosion or erosion on the fluid side will be indicated before such action has 10 progressed beyond the limit of safe wall thickness. More particularly the invention provides a pressure receptacle wall designed to give warning of the wearing away of the inner surface thereof before failure occurs.

Most industrial processes involving the ban dlingof fluids under super-atmospheric pressure are attended with a certain amount of corrosive or erosive action of the fluids upon the inner surfaces of vessels, conduits, valve casings, etc. The reduction of wall thickness by such action will, if allowed to continue, eventually so impair the strength of the wall that failure thereof occurs. When, as is usually the case, the fluids are under high pressure, the danger to life and property resulting from failure of the containing walls is very real.

At the present time it is the practice to inspect plant equipment at regular intervals in order to record the progress of corrosion or erosion. Small holes are bored through the wallsof the various pressure receptacles at a number of points. During the operation of the process the test holes are closed by inserting plugs therein, and during inspection periods the plugs are withdrawnand the thickness of the wall measured. In some instances it is possible to inspect visually the inner surfaces of container walls in addition to measuring the wall thickness. Such precautionary methods are but partially effective in the prevention of accidents due to failure of equipment resulting from the corrosion or erosion of containing walls. The corrosive or erosive effect of fluids upon surfaces in contact therewith is not uniform either as to degree or rate. It is, therefore, difflcult, and sometimes impossible, to accurately gauge the progress of corrosion and the effect thereof in reducing the wall thickness of the industrial vessels or conduits. Particularly is this so in the case of plant equipment used in the refining of petroleum, where both high pressures and high temperatures are frequently encountered. The fluids encountered in such processes are in the main highly corrosive, and it is consequently necessary to take every precaution 55 against the danger of explosion due to failure of receptacles carrying fluids under high pressure. The present invention flnds particular utility in this connection.

According to the present invention a method is provided for treating the walls of pressure re- 00 ceptacles whereby impending failure of the wall due to diminution of its thickness is automatically indicated when the said diminution has progressed to a predetermined degree without the necessity of periodical or. other inspection. Instead of 68 perforating the wall at desired points to provide test holes for the measurement of wall thickness, wells of small diameter are sunk in the wall from the outside thereof at a plurality of points. The thickness of the wall at the said points is there- 70 by reduced, but since the wells are of very small diameter the reduction in the factor of safety at the point of drilling will not materially affect the safe strength of the unit as a whole. As the inner surface of the wall is worn away by corro- 18 sion or erosion, the wall thickness will be reduced beyond the safe limit at the reduced point before the container as a whole is in danger of falling. A break in the wall at the point of reduced thickness will eventually occur and the aperture I thus opened through the wall will allow fluids to escape therethrough. Such a flow from the vessel wall will be an unmistakable indication that the particular section concerned is approaching the limit of safety, and thus replace- '85 ment or reinforcement may be effected before failure can occur.

The location of points at .which the wall thickness of the pressure receptacle is to be reduced will be governed largely by the results of previous observation as to the effect of corrosion in the particular process. The amount of metal to be removed will depend upon the type of vessel involved and the pressure which it is designed to withstand. The diameter of the well resulting from 'a reduction in wall thickness at a particular point need only be large enough to insure th' escape of fluids at a time of complete wearing away of the reduced portion and the formation of an aperture.

The accompanying drawings, in which like reference characters denote like parts, depict the adaptation of the invention to several illustrative types of pressure receptacles. 1n the drawings,

Fig. 1 is a cross sectional view of the wall of 105 a pressure vessel showing the localized reduction of wall thickness according to the invention and depicting the effect of corrosive action upon the inner surface;

Fig. 2 is a perspective view of a tube or pipe, no

the wallof which has been partially perforated to provide for-the anticipation of undue corrosive action on the inside;

Fig. 3 depicts a pipe bend with part in section;

Fig. 4 depicts the treatment of the wall of a valve casing;

Fig. 5 shows a section of sheet metal treated before fabrication in accordance with the method of the invention;

Fig. 6 depicts a particular method of adapting the invention to cast iron fittings in order to prevent undue lowering of the operating strength by reason of the localized reduction in wall thickness;

Fig. 7 illustrates the application of the invention to a furnace tube and to the combined return bend and header box for the same; and

Fig. 8 shows a modified form of return bend and furnace tube treated in anticipation of corrosion.

Referring now to Fig. 1, 10 is a section of the .wall of a pressure receptacle shown in cross section with a well 12 drilled into the wall from the outer side. The initial thickness of the wall is t and the depth of the well 12 is d. The dotted line in the drawings represents generally the wearing away of the inner surface of the wall by reason of the corrosive or erosive action of the fluids in contact therewith. The relation between the depth d of the well 12 and the initial thickness t of the wall 10 will be determined largely by the judgment of the designer which will probably depend upon the necessary factor of safety for the receptacle. In the drawings, d is shown as about one-half of t", but the invention is not limited to the specific reduction in the factor of safety at the point of reduced wall thickness corresponding thereto. Due to the relatively small cross sectional area of the well 12 the danger incident to the localized reduction in the factor of safety is not a reason for particular concern.

It will be noted that as the inner surface of the wall is gradually worn away the wall thickness at the location of the well .12 is reduced below the safe limit long before .the strength of the vessel as a whole has been sufficiently reduced to be susceptible of failure. When the wearing away of the inner surface has progressed to such an extent that an aperture is formed at 12 due to removal of the metal beneath the well, the fluid within the receptacle will escape and in doing so give warning of the extent to which corrosion or erosion has affected the wall as a Whole. In the case of industrial vessels or conduits carrying fluids under very high pressure it is possible for the aperture to be formed at the section of reduced wall thickness, before the metal beneath the well has been entirely eaten away, by a failure of the wall at the small section of reduced thickness. It is unlikely, however, that a break would occur except under exceptionally high pressure since the small diameter of the well 12 will occasion a high degree of resistance of the metal at this point. The net result, however, of such a break at the point indicated would be the same as if the metal had actually worn away to the base of the well, since in either case an aperture is formed in the wall through which fluids may escape to the atmosphere and give warning of the impending danger of failure of the equipment. It is suggested that for moderate pressures a suitable ratio between d and t is 0.5.

As indicated in Fig. 1, the well 12 may advantageously have a conical base. The initial size pipe according to the invention is illustrated.

of the aperture formed upon corrosion of the inner surface of the wall is thereby minimized, while still providing for a perceptible flow through the opening. In this way impairment of the operating strength of the receptacle due to the formation of the aperture is further guarded against. The initial flow or trickle of fluid through the opening 12 will be very small, although sufliciently perceptible to be observed, and the necessary reinforcement or replacement steps may be taken immediately. It may also be desirable in some instances to minimize the total amount of fluid which is allowed to escape from the receptacle either for reasons of economy or for reasons of safety. It is to beunderstood, of course, that the invention is not limited to the particular form discussed above, but that the small wells 12 may have bases which are fiat, hemispherical or any other shape desired.

In Fig. 2, the treatment of a section of straight The flow of fluids through such pipe is usually turbulent and experience has shown that corrosion very frequently causes channels forming spirals on the inner surface of the pipe wall similar to the rifiing of gun barrels. Since it is highly desirable that every section of the wall of a pressure receptacle where maximum corrosion and erosion may be expected should be supplied with a well of the type shown in Fig. 1, Fig. 2, therefore, demonstrates the allocation of the several points of reduced wall thickness in the form of spirals around the outer surface of the pipe.

The adaptation of the invention illustrated in Figs. 3, 4, 5, 6, 7 and 8 is similar in nature to that discussed in connection with Figs. 1 and 2. In Fig. 3 the sections of reduced wall thickness are located at that portion of the curved surface where experience has shown that corrosion is most likely to occur at the most rapid rate. In the 15 treatment of the valve casing shown in Fig. 4 the wells are placed at points in the wall thereof which normally are worn away to the greatest extent. The localized reduction of wall thickness of a sheet of metal intended to be used in the fabrication of a pressure vessel, as, for example,

a bubble tower, is shown in Fig. 5. The allocation of the wells in this instance is determined upon the manner in which the fluids passing through the vessel attack the inner wall as shown by experience.

Fig. 6 depicts a cast iron pipe fitting having a section of the wall thereof reduced in thickness for the purpose of inducing localized failure at this point in indication of the eventual failure of 1 the fitting. The effect of reducing the wall thickness at a particular point in such a fitting upon the operating strength of the fitting itself will probably be more material than the corresponding effect in the case of wrought iron or steel receptacles. In order to compensate for the localized reduction in the factor of safety the outer portion of the wall immediately adjacent the reduced section thereof is built up either by spot welding or by modifying the mold in the process of casting. The additional wall thickness adjacent the weakened section will thus give added strength to the said section during normal operation and prevent cracking, at the same time still providing the fitting with a means for safe-guarding it against complete failure due to corrosion.

The application of the invention shown in Fig. 7 demonstrates the particular utility thereof in connection with the cracking and distilling of petroleum. In Fig. 7, 16 represents a header box 5 having a return bend integral therewith and into which the tube 14 is inserted. The usual practice in assembling such equipment is to expand the end of the tube which is inserted into the header box in order to provide a tight fit as generally illustrated in the drawings. During the operation of the unit corrosion and/or erosion of the tube occurs to the greatest extent at and adjacent to the end at which it is inserted into the header box. The header box itself, in the portion thereof forming the return bend, is also materially affected by such action of the fluids passing therethrough and a failure of either the tube or the header box may very readily occur causing serione property loss and injury to operators. Such a contingency is avoided, according to the present invention, by inducing localized failure of the end of the tube near the header box and/or of the header box itself by reducing the factor of safety at specified points. In the drawings the tube is shown as provided with small wells 12 in the wall thereof at a desired number of points in a circumference of the tube about three inches from the point at which the tube enters the header box. The wall of the header box itself, at the portion of the return bend therein which is most susceptible to corrosion and/or erosion, is also reduced in wall thickness by providing a. well 12 in the wall thereof. The wearing away ofthe inner surfaces will then occasion a localized failure due to the formation of an aperture at the sections of reduced wall thickness in advance of the failure of the whole structure, and such localized failure, while not contributing any dangerous consequences to the operation of the unit, will indicate the impending failure of the equipment. Such indication will probably take the form of smoke issuing from the stack of the furnace or flame within the furnace box.

Fig. 8 is an adaptation of the invention similar to that shown in Fig. 7 and demonstrates the wide applicability of the invention. which is not limited to any specific form of industrial receptacle. In this instance the header box 18 is shown as comprising two sections one of which forms the return bend but the application of the invention is the same as that described in connection with Fig. '7.

-An outstanding advantage of the invention is the simplicity thereof and the ease with which it may be adapted to plant equipment already in use. It is not contemplated, however, that the invention shall be limited to the treatment of fabricated andassembled units, but that pipe sections and sheetmetal' sections intended to be used in the construction of pressure vessels as well as valvecasings and similar containers may be treated during the process of manufacture thereof. Thus, in the construction of a new hubble tower the sheet metal inprocess of fabrication erosion or corrosion with relatively closely spacedweakened areas of small dimension extending inwardly from the external surface of the walls and which ultimately serve, when sufllcient erosion or corrosion has taken place, to produce a leak of hydrocarbon fluid through one of said weakened areas before erosion or corrosion in the affected part has become sumcient to render the part liable to bursting under the pressure of hydrocarbon fluid therein.

2. In a system for the treatment of hydrocarbon oils, a method of anticipating failure due to erosion or corrosion in the walls of containers, conduits or other parts of the system, which comprises providing the walls subject to such erosion or corrosion with relatively closely spaced depressions of small dimension extending inwardly from the external surface of the walls and which ultimately serve, when suflicient erosion or corrosion has taken place, to produce a leak of hydrocarbon fluid through at least one of said depressions before erosion or corrosion of the affected part has become sufllcient to render it liable to bursting under the pressure of hydrocarbon fluid therein.

LUIS DI. FLOREZ. 

